1. Field of the Invention
The present invention relates to a target object gripping apparatus which estimates the orientation of a target object and grips it, a method for controlling the same, and a storage medium.
2. Description of the Related Art
There have been widely developed techniques of imaging the state of a pile of target objects such as parts with a sensor such as a camera, estimating the position or orientation of each target object from acquired information such as an image, and sequentially extracting the target objects by causing a robot to grip them. Japanese Patent Nos. 3225740 and 4226623 disclose techniques of speeding up the processing of gripping target objects.
The technique disclosed in Japanese Patent No. 3225740 is designed to speed up recognition processing by preparing a plurality of matching models for specifying the shape of a target object (part) when a plurality of specific portions of the object assume reference orientations and setting the matching priority order of the models to the descending order of the numbers of times they have been actually recognized at the time of the use of the apparatus.
The technique disclosed in Japanese Patent No. 4226623 is designed to achieve an increase in processing speed and reduce the gripping failure probability for each target object to be selected next by excluding a target object subjected to the failure of the measurement of a three-dimensional position or the failure of extraction from a set of target objects (works) whose coarse positions have been recognized.
In addition, the technique disclosed in Japanese Patent Laid-Open No. 2000-263481 is designed to detect abnormal operations such as a gripping failure based on a change in weight on a 6-axis dynamic sensation sensor and perform subsequent recovery.
In order to sequentially extract target objects from a set of piled target objects, it is necessary to estimate the position and orientation of each target object. It is required from the viewpoint of work efficiency to shorten the time required for position/orientation estimation.
In general, a specific portion of a target object such as part is determined as a portion to be gripped by a manipulator (hand) mounted on the distal end of a robot arm. Depending on the orientation of a target object, therefore, the hand cannot access a specific portion to fail in gripping it. In addition, depending on the orientation of a target object, the information obtained by the sensor may be similar to that of another orientation, and hence erroneous orientation estimation may tend to be performed.
The technique disclosed in Japanese Patent No. 3225740 is designed to achieve an increase in processing speed in consideration of the numbers of times a plurality of specific portions have assumed reference orientations. This technique however gives no consideration to the recognition of erroneous orientations and gripping failures.
The technique disclosed in Japanese Patent No. 4226623 is designed to achieve an increase in processing speed in consideration of coarse positions in case of failure in measuring precise three-dimensional positions and failure in extracting target objects. This technique however gives no consideration to the orientation of a target object having undergone a failure.
The technique disclosed in Japanese Patent Laid-Open No. 2000-263481 is designed to detect abnormality in gripping operation and perform subsequent recovery without calling an operator. That is, this technique is not aimed at speeding up the processing.
That is, conventional techniques have the problem that they give no consideration to the orientation of a target object at the time of failure in gripping the target object.